Most people have two copies of each chromosome, for a total of 46. People with Down syndrome have 3 copies of the 21st chromosome, making a total of 47. Down syndrome is also called Trisomy 21.

which involves the triplication of the 21st chromosome. Celebrated annually on March 21st, this day holds significant importance in highlighting the achievements, challenges, and contributions of ...

Photograph of a karyotype - the collection of chromosomes within each cell of an organism - from a male mouse engineered by Johns Hopkins Medicine researchers to model Down syndrome in a human.